AR~Scorpii is an intermediate polar system composed of a magnetic white dwarf (WD) and an M-type star, and shows non-thermal, pulsed, and highly linearly polarized emission. The radio/optical emission modulates with the WD's spin and show the double peak structure in the light curves. In this paper, we discuss a possible scenario for the radiation mechanism of AR~Scorpii. The magnetic interaction on the surface of the companion star produces an outflow from the companion star, the heating of the companion star surface, and the acceleration of electrons to a relativistic energy. The accelerated electrons, whose typical Lorentz factor is $\sim 50-100$, from the companion star move along the magnetic field lines toward the WD surface. The electrons injected with the pitch angle of $\sinθ_{p,0}>0.05$ are subject to the magnetic mirror effect and are trapped in the closed magnetic field line region.We find that the emission from the first magnetic mirror points mainly contributes to the observed pulsed emission and the formation of the double-peak structure in the light curve. For the inclined rotator, the pulse peak in the calculated light curve shifts the position in the spin phase, and a Fourier analysis exhibits a beat frequency feature, which are consistent with the optical/UV observations. The pulse profile also evolves with the orbital phase owing to the effect of the viewing geometry. The model also interprets the global features of the observed spectral energy distribution in radio to X-ray energy bands. We also discuss the curvature radiation and the inverse-Compton scattering process in the outer gap accelerator of the WD in AR Scorpii and discuss the possibility of the detection by future high-energy missions.
The binary system AR Scorpii hosts an M-type main sequence cool star orbiting around a magnetic white dwarf in the Milky Way Galaxy. The broadband non-thermal emission over radio, optical and X-ray wavebands observed from AR Scorpii indicates strong modulations on the spin frequency of the white dwarf as well as the spin-orbit beat frequency of the system. Therefore, AR Scorpii is also referred to as a white dwarf pulsar wherein a fast spinning white dwarf star plays very crucial role in the broadband non-thermal emission. Several interpretations for the observed features of AR Scorpii appear …
We report a study of the X-ray emission from the white dwarf/M-type star binary system AR Scorpii using archival data taken in 2016-2020. It has been known that the X-ray emission is dominated by the optically thin thermal plasma emission, and its flux level varies significantly over the orbital phase. The X-ray emission also contains a component that modulates with the beat frequency between the white dwarf's spin frequency and orbital frequency. In this new analysis, the 2020 data taken by NICER shows that the X-ray emission is modulating with the spin frequency as well as the beat frequency…
In this work, we have analyzed the $γ$-ray data in the energy range 100 MeV to 500 GeV from the \emph{Fermi}-Large Area Telescope (LAT) observations for the period August 4, 2008 to March 31, 2019. The $γ$-ray emission from AR Scorpii over the last decade is not statistically significant and therefore 2$σ$ upper limit on the integral flux above 100 MeV has been estimated. We reproduce the non-thermal broadband spectral energy distribution of AR Scorpii using an emission model having two synchrotron components due to the relativistic electrons in very high magnetic fields. The first component (…
AR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network (EVN) at 5 GHz and the Chinese VLBI Network (CVN) plus the Warkworth 30-metre telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax ($π=8.52_{-0.07}^…
We analyze rapid-cadence, multiwavelength photometry of AR Scorpii from three observatories, covering five observing seasons. We measure the arrival times of the system's beat pulses and use them to compute an updated ephemeris. The white dwarf spin-down rate is estimated with an uncertainty of only 4%. These results confirm, beyond any doubt, that the white dwarf's spin period is increasing at the rate consistent with by that of Stiller et al. (2018). We study the evolution of the beat pulse's color index across the orbit. The color of the primary pulse maxima varies significantly across the …
Orbital Period Changes of Recurrent Nova U Scorpii Demonstrate that M$_{\rm ejecta}$=26$\times$M$_{\rm accreted}$ and Is Not a Type Ia Supernova Progenitor
A half-ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant
Institute of Science and Technology Austria（奥地利科学技术研究院）；Division of Physics, Mathematics and Astronomy, California Institute of Technology（加州理工学院物理、数学与天文系）；Center for Astrophysics — Harvard & Smithsonian（哈佛-史密森尼天体物理中心）；Mathematical Sciences Institute, The Australian National University（澳大利亚国立大学数学科学研究院）；International Center for Radio Astronomy Research, Curtin University（科廷大学国际射电天文研究中心）；Department of Physics and Astronomy, University of British Columbia（不列颠哥伦比亚大学物理与天文系）；Department of Astronomy & Institute for Astrophysical Research, Boston University（波士顿大学天文系及天体物理研究所）；TAPIR, Mailcode 350-17, California Institute of Technology（加州理工学院TAPIR）
Magnetically powered outbursts from white dwarf mergers
一颗白矮星双星的合并产生了一个差异旋转的物体，预计会产生强大的磁场。储存在差速旋转的动能部分耗散在磁主导的日冕，形成一个热的可变流出与喷射速度相当于$10^9$厘米秒$^{-1}$。流出物应该会携带大量的质量和能量持续数小时到数天，形成一个具有以下特征的膨胀火球。(i)火球最初是不透明的，它的内能主要是由被捕获的热辐射。储存的热量部分地转换为流的动能（通过绝热冷却）并部分地辐射出去。(ii)内部冲击在火球中发展并增加其辐射输出。(iii)发射能量的很大一部分在光学波段。因此，从合并中可以预期亮度为$L\sim 10^{41}-10^{42}$ erg s $^{-1}$且特征峰持续时间相当于1天的明亮光学瞬变。与经典新星或超新星不同，瞬变不涉及核能。峰值后的衰减反映了合并残留物中的差异旋转的阻尼。这样的爆发可以在当前和即将到来的光学调查中在本地宇宙中检测到。
I discuss elastic properties of neutron star crust in the framework of static Coulomb solid model when atomic nuclei are treated as non-vibrating point charges; electron screening is neglected. The results are also applicable for solidified white dwarf cores and other materials, which can be modeled as Coulomb solids (dusty plasma, trapped ions, etc.). I demonstrate that the Coulomb part of the stress-strain tensor has additional symmetry: contraction $B_{ijil}=0$. It does not depend on the structure (crystalline or amorphous) and composition. I show as a result of this symmetry the effective …
